It's not the fault of the average American that they are unaware of the massive contribution made by the British and their Commonwealth.
It's the fault of your film and TV producers who think that the only way they can attract American audiences is to only show what the USA did in the war. I think that is an insult to American intelligence!
Very few Americans are aware of Bletchley Park (whose code-breakers shortened the war by two years by breaking all the German codes and they also broke the Japanese Red/Blue/Purple codes in 1941 and passed the details to Washington).
How many Americans are aware of the British Pacific Fleet that fought at Tarawa, Okinama etc? 20 Aircraft Carriers, 6 Battleships, 25 Cruisers and hundreds of other vessels.
Did you know that in 1942, the USA had no fighter able to combat the German ME109 on equal terms? The British lent you 600 Spitfires (read "Uncle Sam's Spitfires!)
But, apart from all that, you're a lovely people and I am treated so well every time I visit the USA (common question in the South -Y'all not from around here?)